The present invention pertains to a device for simultaneously and continuously monitoring both the impedance of a trip coil and the voltage across a capacitor used to actuate the trip coil, and pertains more specifically to a sensor device for use with a coil and capacitor used in conjunction with equipment that must be maintained at voltages into the UHV range (5-2,000 kV).
Circuit breakers are known in which a trip coil, or Lenz coil is used to operate the interrupter. Such a system comprises a Lenz coil and a movable repulsion disc magnetically coupled to the Lenz coil. The movable disc is usually fixed to or is an integral part of the movable contact of the interrupted. To actuate the interrupted, a large current is suddenly caused to pass through the Lenz coil, producing a strong repulsive force between the Lenz coil and the movable repulsion disc in accordance with Lenz's law.
A very fast initial response can be obtained using an operating mechanism of this type, and such mechanisms are highly controllable, making them very suitable for use in the synchronous type of circuit breaker. A Lenz coil system, however, can provide high acceleration only for a short time since, as the gap between the disc and the coil increases, the net repulsive force between them decreases very rapidly. To overcome this deficiency, it is possible to add a mechanical assist to the system so that the opening force can be maintained at a high level for a longer time. For example, it is well known to couple a pneumatic system to an electrodynamically operated system for operating a circuit interrupter, as shown for example in U.S. Pat. No. 4,209,680, issued June 24, 1980, to Ruben D. Garzon for a HIGH SPEED ACTUATING MECHANISM, and U.S. Pat. No. 3,821,506, issued June 28, 1974, to Lorne D. McConnell, for an INFLATED VALVE SEAT FOR SYNCHRONOUS BREAKERS. Both of these patents are assigned to the assignee of the present application.
In circuit breaker operating mechanisms employing a Lenz coil, it is desirable to monitor the capacitor to ensure that a sufficient amount of energy is stored therein to actuate the opening stroke of the interrupter, as well as to monitor the trip coil to ensure that no damage has occurred to it during previous operation of the interrupter. Conventional monitoring equipment is relatively cumbersome. In addition, since the capacitor and the trip coil are at the potential of the line in which the interrupter is placed, it is necessary to isolate the monitoring equipment, which must be at the same high potential as the capacitor and trip coil, from ground potential. On the other hand, a device must be provided to indicate the condition of the capacitor and trip coil to personnel. This device must clearly be at ground potential. To isolate the monitoring equipment proper from the status indicating device at ground potential, an isolation transformer is commonly used. Such a transformer is relatively bulky and expensive. Moreover, in the event of a transformer breakdown, there is a danger that the isolation between the monitoring device proper and the status indicating device at ground potential may be degraded, with the resulting possibility of serious or even fatal injury to personnel.